Newborn hearing screening
What is a newborn infant hearing screening program?Newborn infant hearing screening programs are designed to identify hearing loss in infants shortly after birth within hospitals and birthing clinics. Most hearing screening tests are done prior to discharge from the hospital or birthing clinics.
How is hearing in infants tested?
Hearing in infants can be tested using two different methods: the auditory brainstem response (ABR) evaluations or the otoacoustic emission (OAE) measures. Both tests are accurate, noninvasive, automated, and do not require any observable response from the infant. Which test is used depends on the screening program's choice of instrumentation and training. For a screening tool, both methods are extremely effective. There are, however, some distinct differences in how the hearing is measured using an ABR versus an OAE.
What is an ABR test?
An auditory brainstem response (ABR) is a physiological measure of the brainstem's response to sound. It tests the integrity of the hearing system from the ear to the brainstem. The test is performed by placing four to five electrodes on the infant's head, after which a variety of sounds is presented to the infant through small earphones. As the hearing nerve fires, the sound stimulus travels up to the brain. This electrical activity generated by the nerve can be recorded by the electrodes and is represented as waveforms on a computer screen. The audiologist can then present different loudness levels of each sound and determine the softest levels at which the infant can hear. For infant-screening purposes, only one sound is used to test the hearing, commonly referred to as a "click." The click is a grouping of several sounds to test a wider area of the hearing organ at one time. The click is typically presented at a loud level and a soft one. If a healthy response is recorded, then the infant has "passed" the hearing screen. Testing usually takes five to 15 minutes to complete.
What is an OAE evaluation?
An otoacoustic emission test (OAE) measures an acoustic response that is produced by the inner ear (cochlea), which in essence bounces back out of the ear in response to a sound stimulus. The test is performed by placing a small probe that contains a microphone and speaker into the infant's ear. As the infant rests quietly, sounds are generated in the probe. Once the cochlea processes the sound, an electrical stimulus is sent to the brainstem. In addition, there is a second and separate sound that does not travel up the nerve but comes back out into the infant's ear canal. This "byproduct" is the otoacoustic emission. The emission is then recorded with the microphone probe and represented pictorially on a computer screen. The audiologist can determine which sounds yielded a response/emission and the strength of those responses. If there is an emission present for those sounds that are critical to speech comprehension, then the infant has "passed" the hearing screen. Testing generally takes about five to eight minutes.
What does it mean when an infant does not pass the hearing screen?
A newborn who fails an initial hearing screen may not necessarily have a permanent hearing loss or a hearing loss at all. There are many possible reasons why an infant may fail a hearing screening test. One common reason is that fluid from the birth may still be present in the ear canal. This fluid blocks the sound stimulus, preventing it from reaching the inner ear, and therefore causes the newborn to fail. Similarly, fluid in the middle-ear space behind the eardrum (a common site for infection in children) can also block the sound stimulus and lead to a false failed test. After these problems resolve, the infant usually passes the rescreen. Therefore, it is important to have at least one week between the initial hearing screen and the rescreen to allow the newborn a chance to "dry out." Another possible reason for a false failure is excessive noise or movement from the infant during the test. The responses that are recorded with an ABR or OAE are very, very small. Any movement or crying from the infant can prevent the equipment from detecting the response. Therefore, it is important that the newborn is quiet or sleeping for the hearing screen. Feeding the infant just prior to the screening is often very helpful. If it becomes evident that an infant has a hearing loss, then a full diagnostic exam is necessary to determine the type and amount of hearing loss.
If an infant does not pass a hearing screen in the hospital, what happens next?
Most hospital screening programs will refer infants who failed the initial screening test to a secondary center that specializes in more complete testing for diagnosis. Sometimes, simple problems, such as too much residual amniotic fluid and vernix in the ear canal, will resolve prior to the rescreen and the infant will pass the second test. The rescreen is an important step in determining whether the infant is able to hear, so it should not be taken lightly.
If an infant does not pass the rescreen, then a full diagnostic test will be necessary. This test may be completed at the rescreen site or at another facility, depending on several factors.
If an infant has a hearing loss, what is the next step?
The ability of an infant to compensate for the hearing loss will depend on both the type and the degree of hearing loss. The type of hearing loss refers to where in the ear the hearing loss is located and what is causing it. There are two basic types of hearing loss, conductive and sensorineural. A conductive loss is caused by problems in the outer or middle ear. This is the type of loss that results when a child has a middle-ear infection, trapped fluid from birth, impacted wax in the outer ear or malformation of the ear and associated structures. It is usually correctable with medical treatment or surgery. Occasionally, a conductive loss cannot be corrected with surgery. However, these children typically do extremely well with hearing aids. A sensorineural loss is indicative of a problem in the inner ear or somewhere along the nerve to the ear (auditory nerve). This type of loss is typically permanent and cannot be corrected with surgery. A hearing aid or a cochlear implant may be utilized in this situation.
The degree of hearing loss refers to the severity of the hearing loss, which can range from mild to profound. Although the term "mild" sounds relatively benign, a mild hearing loss in a child who is trying to develop speech and language can have a huge impact on his/her success.
If the hearing loss, whether it is conductive, sensorineural, or a combination of both, is determined to be uncorrectable by a physician, then the next step is to fit the infant with hearing aids. This is accomplished by a pediatric audiologist who can adjust the hearing aids according to the baby's hearing loss and monitor the infant's progress through regular visits. The infant should also be enrolled in an early childhood intervention program that is often provided through the school system.
In addition to the early medical or surgical treatment of the hearing loss, parental involvement is essential. Parents need to monitor the child's progress and facilitate and encourage the use of the hearing aids and other therapeutic exercises that are designed to help the child become a careful listener and talker. Research has found that the one common denominator among successful hearing-impaired children is the parent's willingness to help the child throughout his/her lifetime.